Phylogenetic and physiological characterization of indigenous azospirillum isolates in Thailand

Abstract

We isolated indigenous Azospirillum bacteria in Thailand and analyzed the physiological characteristics and phylogenetic properties of the 16S rDNA sequences. Azospirillum bacteria were isolated from the rhizosphere soil and surface-sterilized root samples of nonleguminous plants, such as sugarcane, vetiver grass, wild rice, sweet potato, maize, and cultivated rice, grown in Thailand. Nitrogenase activity evaluated by the acetylene reduction activity (ARA) and indole-3-acetic acid (IAA) production enabled to classify the Thai isolates into two groups: Group I, which showed a high lAA production, and Group II, which showed a low ARA and lAA production. Phylogenetic analysis of the 16S rDNA sequences revealed that the 12 isolates in Group I were closest to Azospirillum largimobile, with 97 to 99% homology values, and they were also close to Azospirillum brasilense. The 16S rDNA sequence of TS18 in Group II was distant from all seven known species in the genus Azospirillum, indicating that TS18 may belong to a new species of Azospirillum. Analyses of other physiological characteristics, such as colony morphology, biotin requirement, carbon utilization, and acid formation, also revealed the existence of specificity and diversity among the Thai Azospirillum isolates.